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Abstract:

A power transmission device for a four-wheel drive vehicle having a power
source and first and second drivelines includes an input shaft adapted to
be driven by the power source. A first output shaft is rotatable about a
first axis and adapted to transmit torque to the first driveline. A
second output shaft is adapted to transmit torque to the second driveline
and is rotatable about a second axis. The first and second axes do not
extend parallel to each other. A transfer unit includes a first
cylindrically-shaped gear rotatably supported on the first output shaft
and a second conically-shaped gear fixed for rotation with the second
output shaft. The first and second gears are in constant meshed
engagement with each other.

Claims:

1. A power transmission device for use in a four-wheel drive vehicle
having a power source and first and second drivelines, the power
transmission device comprising:an input shaft adapted to be driven by the
power source;a first output shaft being rotatable about a first axis and
adapted to transmit torque to the first driveline;a second output shaft
adapted to transmit torque to the second driveline, the second output
shaft being rotatable about a second axis, wherein the first and second
axes do not extend parallel to each other; anda transfer unit having a
first cylindrically-shaped gear rotatably supported on the first output
shaft and a second conically-shaped gear fixed for rotation with the
second output shaft, the first and second gears being in constant meshed
engagement with one another.

2. The power transmission device of claim 1 further including a clutch
selectively operable to transfer drive torque between the first output
shaft and the first gear, and a clutch actuation system operable to
control the clutch.

3. The power transmission device of claim 2 wherein the clutch is a
friction plate clutch having a first set of friction elements fixed for
rotation with the first output shaft and a second set of friction
elements being fixed for rotation with the first gear.

4. The power transmission device of claim 3 wherein the clutch actuation
system includes a rotary to linear movement conversion mechanism.

5. The power transmission device of claim 4 wherein the rotary to linear
movement conversion mechanism includes a ball ramp unit including a pair
of cam rings spaced apart by a plurality of rolling elements.

6. The power transmission device of claim 3 wherein the torque transferred
by the clutch may be varied to transfer different magnitudes of torque to
each of the first and second drivelines.

7. The power transmission device of claim 1 wherein the first and second
axes of rotation define an included angle of substantially seven degrees.

8. The power transmission device of claim 1 further including a cardan
joint positioned within a cavity formed in the second gear.

9. The power transmission device of claim 1 further including a
differential assembly operably positioned between the first and second
output shafts.

10. A power transmission device for use in a four-wheel drive vehicle
having a power source and first and second drivelines, the power
transmission device comprising:an input shaft adapted to be driven by the
power source;a first output shaft being rotatable about a first axis and
adapted to transmit torque to the first driveline;a second output shaft
adapted to transmit torque to the second driveline, the second output
shaft being rotatable about a second axis, wherein the first and second
axes diverge from one another;a transfer unit having a first gear
rotatably supported on the first output shaft and a second gear coupled
to the second output shaft, the first and second gears being in constant
meshed engagement with one another; anda universal joint positioned
within a cavity formed in the second gear and drivingly interconnecting
the second gear and the second output shaft.

11. The power transmission device of claim 10 further including a clutch
selectively operable to transfer drive torque between the first output
shaft and the first gear, and a clutch actuation system operable to
control the clutch.

12. The power transmission device of claim 10 wherein the first gear
includes cylindrically-shaped teeth engaging conically-shaped teeth
formed on the second gear.

13. The power transmission device of claim 10 wherein the first and second
axes intersect at a point.

14. The power transmission device of claim 10 wherein the input shaft and
the second output shaft are positioned on a first side of the power
transmission device, the first output shaft being positioned on an
opposite second side.

15. The power transmission device of claim 10 wherein the first and second
axes of rotation define an included angle of substantially seven degrees.

Description:

FIELD

[0001]The present disclosure relates generally to a power transmission
device for use in a motor vehicle. More particularly, the present
disclosure describes a compact transfer case having crossed axis output
shafts for providing drive torque to first and second drivelines of a
four-wheel drive vehicle.

BACKGROUND

[0002]Many sport-utility vehicles are equipped with a transfer case for
transmitting drive torque to all four of the wheels, thereby establishing
a four-wheel drive mode of operation. Some transfer cases are equipped
with a mode shift mechanism which permits the vehicle operator to
selectively shift between a two-wheel drive mode wherein only the primary
(i.e., rear) driveline is driven and a "part-time" four-wheel drive mode
wherein the secondary (i.e., front) driveline is rigidly coupled for
rotation with the primary driveline.

[0003]In the past, the vehicle ride height and suspension configuration of
many sport-utility vehicles provided sufficient packaging volume for a
traditional transfer case having at least two rotating output shafts
extending parallel to one another. In view of increased consumer demand
for smaller four-wheel drive vehicles, the packaging volume allocated to
the vehicle powertrain has been greatly reduced. While traditional
transfer case designs may function in a satisfactory manner in certain
vehicle applications, a need for an improved, compact, light weight power
transmission device exists.

SUMMARY OF THE INVENTION

[0004]A power transmission device for a four-wheel drive vehicle having a
power source and first and second drivelines includes an input shaft
adapted to be driven by the power source. A first output shaft is
rotatable about a first axis and adapted to transmit torque to the first
driveline. A second output shaft is adapted to transmit torque to the
second driveline and is rotatable about a second axis. The first and
second axes do not extend parallel to each other. A transfer unit
includes a first cylindrically-shaped gear rotatably supported on the
first output shaft and a second conically-shaped gear fixed for rotation
with the second output shaft. The first and second gears are in constant
meshed engagement with each other.

[0005]The present disclosure also provides a power transmission device for
use in a four-wheel drive vehicle having a power source and first and
second drivelines. The power transmission device includes an input shaft
adapted to be driven by the power source. A first output shaft is
rotatable about a first axis and is adapted to transmit torque to the
first driveline. A second output shaft is adapted to transmit torque to
the second driveline and is rotatable about a second axis. The first and
second axes diverge from one another. A transfer unit includes a first
gear rotatably supported on the first output shaft and a second gear
coupled to the second output shaft. The first and second gears are in
constant meshed engagement with one another. A universal joint is
positioned within a cavity formed in the second gear and drivingly
interconnects the second gear and the second output shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]The disclosure will now be described, by way of example, with
reference to the accompanying drawings in which:

[0007]FIG. 1 is a schematic illustrating the drivetrain of a motor vehicle
equipped with a power transmission device of the present disclosure;

[0008]FIG. 2 is a cross-sectional view of the power transmission device
according to the present disclosure;

[0009]FIG. 3 is a cross-sectional view of an alternative power
transmission device associated with the drivetrain shown in FIG. 1; and

[0010]FIG. 4 is a cross-sectional view of another alternative power
transmission device associated with the drivetrain shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011]In general, the present disclosure relates to a power transmission
device for a motor vehicle having a first output shaft rotatable about a
first axis and a second output shaft that rotates about a second axis of
rotation. The first and second axes cross one another. A clutch actuation
system may operate a clutch associated with the first and second output
shafts of the power transmission device for selectively or automatically
shifting between a four-wheel drive mode and a two-wheel drive mode. A
gearset including a beveloid gear transfers power between the first
output shaft and the second output shaft.

[0012]With particular reference to FIG. 1 of the drawings, a drivetrain 10
for a four-wheel drive vehicle is shown. Drivetrain 10 includes a front
driveline 12 and a rear driveline 14 both drivable from a source of
power, such as an engine 16, through a transmission 18 which may be of
either the manual or automatic type. In the particular embodiment shown,
drivetrain 10 is a four-wheel drive system which incorporates a power
transmission device 20 for transmitting drive torque from engine 16 and
transmission 18 to front driveline 12 and rear driveline 14. Front
driveline 12 is shown to include a pair of front wheels 24 connected at
opposite ends of a front axle assembly 26 having a front differential 28
that is coupled to one end of a front propeller shaft 30 by a universal
joint 31. The opposite end of front propeller shaft 30 is coupled to a
second or front output shaft 32 of power transmission device 20.
Similarly, rear driveline 14 includes a pair of rear wheels 34 connected
at opposite ends of a rear axle assembly 36 having a rear differential 38
coupled to one end of a rear propeller shaft 40, the opposite end of
which is interconnected to a first or rear output shaft 42 of power
transmission device 20.

[0013]With particular reference to FIG. 2 of the drawings, power
transmission device 20 is shown to include an input shaft 44 adapted for
connection to an output shaft 46 of transmission 18 such that both are
rotatably driven by engine 16 of the motor vehicle. In the arrangement
depicted, rear output shaft 42 is integrally formed with input shaft 44
as a one-piece first shaft 48 that is rotatably supported in a housing
assembly 50. Front output or second shaft 32 is also rotatably supported
in housing assembly 50.

[0014]A transfer assembly 54 is provided for selectively transferring
drive torque from first shaft 48 to second shaft 32. Transfer assembly 54
includes a first or drive gear 56 rotatably supported on first shaft 48
and a second or driven gear 58 in constant meshed engagement with drive
gear 56. Driven gear 58 is fixed for rotation with second shaft 32.
Alternatively, driven gear 58 and second shaft 32 may be formed as a
single monolithic one-piece member. Housing assembly 50 includes
separable first, second and third housings 60, 62 and 64, respectively.
Driven gear 58 is rotatably supported within first housing 60 by a first
tapered roller bearing 66. Driven gear 58 is also supported for rotation
by a second tapered roller bearing 68 positioned within second housing
62.

[0015]First shaft 48 is rotatable about a first axis 70. Second shaft 32
is rotatable about a second axis 72. First axis 70 and second axis 72
diverge from one another and define an included angle A. In the Figures,
first axis 70 intersects second axis 72. It is also envisioned that
second axis 72 may be skew to first axis 70 such that the axes never
intersect. Regardless, angle A may be defined by viewing power
transmission device 20 as shown in FIG. 2 where a viewing plane of the
page includes first axis 70 and a point along second axis 72 that is
centered within the gear tooth width. Front propeller shaft 30 is
positioned substantially coaxially with second shaft 32 and extends at
approximately angle A relative to second propeller shaft 40. By
positioning front output shaft 32 at an angle to rear output shaft 42, an
overall height B of housing assembly 50 may be minimized. This may be
accomplished because front propeller shaft 30 diverges from engine 16 and
transmission 18 as front propeller shaft 30 approaches front drive axle
26. A large offset between drive and driven sprockets interconnected by a
chain is no longer required. In the example depicted in FIGS. 1 and 2,
angle A is substantially seven degrees.

[0017]To provide means for establishing a drive connection between first
shaft 48 and second shaft 32, power transmission device 20 includes a
mode shift mechanism 90. Mode shift mechanism 90 includes a mode clutch
92 which is operable to couple drive gear 56 to first shaft 48 for
establishing a four-wheel drive mode in which second shaft 32 is rigidly
coupled for rotation with first shaft 48. In addition, mode clutch 92 is
operable for selectively decoupling drive gear 56 from first shaft 48 for
establishing a two-wheel drive mode in which all drive torque is
delivered to rear output shaft 42.

[0018]According to the embodiment shown in FIG. 2, mode clutch 92 is
normally operable in a non-actuated mode for transmitting all drive
torque to rear output shaft 42, thereby establishing the two-wheel drive
mode. Mode clutch 92 is also operable in a fully-actuated mode for
establishing a "locked" four-wheel drive mode in which front output shaft
32 is rigidly coupled to rear output shaft 42. In the embodiment shown in
FIG. 2, mode clutch 92 is a friction plate clutch. Mode clutch 92 may be
controlled to progressively regulate the amount of torque transferred to
front output shaft 32 automatically (i.e., on-demand) between its
non-actuated and fully-actuated modes in response to and as a function of
the amount of relative rotation (i.e., interaxle slip) between front
output shaft 32 and rear output shaft 42. The torque versus slip
characteristics of mode clutch 92 can be tuned to meet specific vehicular
applications.

[0019]Mode clutch 92 includes an inner hub 94 fixed to first shaft 48 and
to which a set of inner clutch plates 96 are fixed. Mode clutch 92 also
includes a drum 98 fixed for rotation with drive gear 56. Drum 98 is
cylindrical and has a set of outer clutch plates 100 fixed thereto which
are alternately interleaved with inner clutch plates 96 to define a
multi-plate clutch pack. Other physical arrangements of mode clutch 92
(not shown) may perform the same function and are contemplated as being
within the scope of the present disclosure.

[0020]A clutch actuation system 106 controls mode clutch 92. Clutch
actuation system 106 includes an actuator 110 and may also include a
rotary to linear movement conversion mechanism 112. In particular,
actuator 110 includes a drive motor 114 for rotating a drive shaft 116.
Drive shaft 116 is coupled to rotary to linear movement conversion
mechanism 112. Rotary to linear movement conversion mechanism 112
includes a ball ramp unit 120. Ball ramp unit 120 includes a pair of cam
rings 122, 124 and a plurality of balls 126. Each of cam rings 122 and
124 include grooves 128 and 130, respectively. Grooves 128 and 130 have
varying depths. Balls 126 are positioned within grooves 128 and 130. When
balls 126 are positioned at the deepest portion of grooves 128 and 130,
cam rings 122 and 124 are spaced apart a first distance from one another.
Cam ring 124 is rotatable relative to cam ring 122 to cause balls 126 to
be positioned within the shallow portion of grooves 128 and 130. At this
position, cam rings 122 and 124 are spaced apart from one another a
distance greater than the first distance. In this manner, ball ramp unit
120 is operable to convert rotary motion to linear motion.

[0021]In operation, clutch actuation system 106 is controlled to apply a
force on the mode clutch 92. Drive motor 114 rotates drive shaft 116 in a
first direction which rotates cam ring 124 relative to cam ring 122 to
axially move cam ring 122 and apply a force to an apply plate 132. Inner
clutch plates 96 are frictionally engaged with outer clutch plates 100 by
apply plate 132 to transfer drive torque from rear output shaft 42 to
front output shaft 32. Rotating drive motor 114 in the reverse direction
rotates cam ring 124 back to a start position thereby removing the
application force from mode clutch 92. Thus, second shaft 32 is no longer
driven by first shaft 48. Alternatively, actuator 110 need not be
configured to include a drive motor but may utilize other force
transmitting mechanisms as appropriate. Furthermore, it should be
appreciated that the clutch actuation system previously described may be
replaced with a variety of other force application devices including
hydraulically or electrically powered pumps acting on one or more
pistons, motors driving one or more gearsets and power screws, among
others.

[0022]FIG. 3 depicts another power transmission device identified at
reference numeral 200. Power transmission device 200 is substantially
similar to power transmission device 20. Accordingly, similar elements
will be identified with like reference numerals including a prime suffix.
Power transmission device 200 differs from device 20 in that an
additional degree of freedom has been provided to front output shaft 32'
to allow the front output shaft to articulate about a point positioned
within power transmission device 20. The additional degree of freedom may
allow a further reduction in the overall height of power transmission
device 200 and allow positioning of the device within even further
constrained packaging envelopes.

[0023]Power transmission device 200 includes a conical driven gear 202 in
constant meshed engagement with cylindrical drive gear 56'. Driven gear
202 is a two-part assembly including a first portion 204 fixed to a
second portion 206. First portion 204 includes a plurality of conically
shaped gear teeth 208 in constant meshed engagement with teeth 80'. First
portion 204 also includes a first hub 210 supported for rotation by an
angular contact bearing 212. Angular contact bearing 212 may include
tapered rollers, balls or a variety of other configurations designed to
accurately support driven gear 202 for rotation within second housing 62'
as well as react substantial axial loading generated due to the conical
shape of teeth 208.

[0024]Second portion 206 includes a second hub 214 supported for rotation
by another angular contact bearing 216. Angular contact bearing 216 is
supported by first housing 60'. A seal assembly 218 restricts
contaminants from entering housing assembly 50' while allowing driven
gear 202 to rotate relative thereto. Second portion 206 also includes a
snout 220 protruding from housing assembly 50' to provide an attachment
land for a boot (not shown). The boot sealingly interconnects front
output shaft 32' and snout 220 to restrict contamination from entering a
cavity 222 defined by first portion 204 and second portion 206.

[0025]A single cardan universal joint 224 is positioned within cavity 222.
Universal joint 224 includes a first yoke 226 fixed to a stub shaft 228.
First yoke 226 and stub shaft 228 are fixed for rotation with driven gear
202. Universal joint 224 also includes a second yoke 232 drivingly
coupled to first yoke 226 by a cruciform 234. Cruciform 234 includes two
pairs of trunnions. One pair of trunnions is supported for rotation by
first yoke 226 and the second pair of trunnions is supported for rotation
by second yoke 232. One end of front output shaft 32' is fixed for
rotation with second yoke 232. Through this arrangement, torque is
transferred from driven gear 202 through first yoke 226, cruciform 234,
second yoke 232 to front output shaft 32'. Front output shaft 32' may
rotate about an axis other than the axis about which driven gear 202
rotates.

[0026]By constructing power transmission devices 20 and 200 as previously
described, a family of transfer cases may be defined where a first member
of the family includes the components shown in FIG. 1. Another alternate
family member may include an alternate first housing and an alternate
second housing to rotatably support a driven sprocket or gear rotatable
about an axis parallel to axis 70 if the vehicle packaging envelope so
allows.

[0027]A further modular approach includes assembling a power transmission
device 300, shown in FIG. 4, using first housing 60 and second housing 62
as well as the components positioned therein as shown in FIG. 1. An
alternate third housing 302 may replace third housing 64. A module 304 is
positioned with third housing 302 and replaces mode clutch 92. Module 304
includes one or more of a center differential, a "part-time" mode clutch,
a gearset for providing two or more drive ratios and a pump for providing
a clutch actuation force. The part-time clutch may be configured as a
stand-alone dog clutch or may comprise a synchronizer cooperating with
the dog clutch. Module 304 may also include an actuator for operating the
components within third housing 302.

[0028]The foregoing discussion discloses and describes various embodiments
of the present disclosure. One skilled in the art will readily recognize
from such discussion, and from the accompanying drawings and claims, that
various changes, modifications and variations can be made therein without
departing from the true spirit and fair scope of the disclosure as
defined in the following claims.